SYDNEY/COLOMBO, July 4 (Reuters) - The United Nations has expressed "profound concern" about Australia's handling of asylum seekers amid reports that scores of Sri Lankans will be handed over to their country's navy after only a brief assessment by Australian authorities.

Two boats carrying more than 200 Tamil asylum seekers from Sri Lanka were intercepted by Australian border security forces in the Indian Ocean in recent days and either have been or will be transferred to the Sri Lankan navy, Australian media said.

An Australian source with knowledge of the operation said the intention was to carry out the transfer on Friday, but the situation was fluid.

The prospect of a risky mid-ocean transfer of Tamil asylum seekers and their return to Sri Lanka has sparked criticism of Australia's tough immigration policy.

Sri Lanka is facing heavy pressure from rights groups and the West for alleged human rights violations during the final phase of the war against Tamil separatists which ended in 2009.

It says many asylum seekers are economic migrants, but rights groups say Tamils seek asylum to prevent torture, rape and other violence at the hands of the military.

Australia's government has not confirmed any details of the incident and refuses to comment on what it calls operational matters regarding its "Operation Sovereign Borders" programme.

PERSECUTION FEARS

The UNHCR said it did not have official confirmation of the incidents but said it had followed "with profound concern recent reports in the media and from the community" about interceptions and assessment of claims for asylum.

"International law prescribes that no individual can be returned involuntarily to a country in which he or she has a well-founded fear of persecution," UNHCR said in a statement late on Thursday.

Sri Lankan officials have given conflicting accounts about whether their navy has been involved, while the Foreign Ministry and Immigration and Emigration department have both claimed the other was responsible for the return of illegal migrants.

Government spokesman Keheliya Rambukwella said on Thursday that the navy had agreed to accept the asylum seekers but changed his response after questioning from reporters.

"I really don't know where we stand," he said.

Two other officials of the government of President Mahinda Rajapaksa said the navy would receive the boat people from its Australian counterpart.

One said a number of former Liberation Tigers of Tamil Eelam (LTTE) rebels were believed to be among the asylum seekers.

"The navy is trying to bring them here because of the fact that there are a large number of LTTE cadres," he said.

Ian Rintoul, a coordinator for Australia's Refugee Action Coalition, was in contact with some asylum seekers on one of the boats until last Saturday. Nothing had been heard from those on the vessel since then and concerns were mounting that anyone suspected of having ties to the LTTE would face harsh treatment if returned to Sri Lanka.

"There have certainly been things that have come out of India that have indicated that there could be people with Tiger affiliations on that boat and that would certainly whet the appetite of the Rajapaksa regime to put their hands on those people," Rintoul said.

Australian Prime Minister Tony Abbott, who came to power last September partly because of his tough stance on asylum seekers, has declined to comment, saying only that it was no secret that boats had been turned back under the policy.

"I want to make this observation," he said. "Sri Lanka is not everyone's idea of an ideal society, but it is at peace."

In the past three months, three Tamil asylum seekers on temporary visas in Australia, facing the prospect of being returned to Sri Lanka, have set themselves on fire. Two died.

While Abbott's popularity among voters has plummeted, more than 70 percent of Australians support the government's border policy, including sending boats back when safe to do so, according to a recent poll by the Lowy Institute think tank.

Australia has offshore detention centres in the impoverished South Pacific nations of Papua New Guinea and Nauru capable of holding thousands.

About 16,000 asylum seekers came on 220 boats to Australia in the first seven months of last year but the government says there have been no illegal boat arrivals since December 2013. (Additional reporting by Aubrey Belford and Ranga Sirilal; Editing by Nick Macfie and Stephen Coates)